Bug 247454

Summary:	Reduce aliasing of Wasm::Type type index field
Product:	WebKit	Reporter:	David Degazio <d_degazio>
Component:	WebAssembly	Assignee:	David Degazio <d_degazio>
Status:	NEW ---
Severity:	Enhancement	CC:	d_degazio, webkit-bug-importer
Priority:	P2	Keywords:	InRadar
Version:	WebKit Nightly Build
Hardware:	Unspecified
OS:	Unspecified

Description David Degazio 2022-11-03 12:58:47 PDT

The Wasm::Type data structure generated in JavaScriptCore/wasm/generateWasmOpsHeader.py contains a TypeIndex field, which is currently used to store any of the following:
 - TypeDefinition::invalidIndex, for simple/primitive types
 - A TypeKind, specifically Funcref or Externref, used to implement those types when typed function references are enabled
 - A pointer to a TypeDefinition, for compound types like functions or structs

We currently lose 7/16 bytes of Wasm::Type to padding, so it'd be nice to use some of that space (or maybe refactor Wasm::Type in general) to separate these values out into other fields or a union type so we aren't reinterpreting this uintptr_t all the time.

Comment 1 Radar WebKit Bug Importer 2022-11-03 12:59:00 PDT

<rdar://problem/101926680>